Not sure if this is a bug or just really poor design.
Okay, so now there are rules about how many items you can have in your inventory to change subclasses. This is a very poorly made system, the rule is:
* If you are over 80% inventory on your current class, you can't change.
Firstly, unlike questing, subclassing doesn't add items to your inventory so making this change is pretty silly. Secondly, because it uses the current class's max capacity, and not the max capacity of the class you're changing into, it doesn't even help to fix problems where you'd go over 100% items when changing to a new subclass. That's still quite possible to do -- change from a dwarf class with expanded inventory into a non-dwarf class without.
The maximum item capacity of your current class is pretty much totally unrelated to the capacity of the class you're changing into, and as such, even if the developers want to ensure that you won't go over 100% items on subclassing, they didn't accomplish that at all.
The system SHOULD check if your current item count is beyond the maximum item count of the class you're changing into. No 80% nonsense, no using the current class's max capacity in calculations.